Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $195.42   13.749%   $222.2883   $222.29   $222.30   $222.30  
  Purchase #2 $125.59   10.194%   $138.3926   $138.39   $138.40   $138.40  
  Purchase #3 $172.69   13.527%   $196.0498   $196.05   $196.05   $196.00  
  Purchase #4 $240.80   10.484%   $266.0455   $266.05   $266.05   $266.00  
  Purchase #5 $178.70   13.122%   $202.149   $202.15   $202.15   $202.10  
  Purchase #6 $244.94   12.803%   $276.2997   $276.30   $276.30   $276.30  
  Purchase #7 $210.73   6.449%   $224.32   $224.32   $224.30   $224.30  
  7 purchase totals = $1,368.87       $1,525.5449   $1,525.55   $1,525.55   $1,525.40